At least three top drive manufacturers and at least two third-parties offer a top drive accessory known as a Casing Running Tool (herein a CRT). CRT's attach, directly or indirectly, to the top drive quill and enable the top drive (hereinafter also referred to as a “TD”) to hoist, rotat e and circulate casing without screwing into it, which is advantageous as explained below. A CRT grips and seals either on the outside or the inside of the casing.
In the prior art, applicant is aware of Tesco™ U.S. Pat. Nos. 7,140,443 and 7,377,324, and Tesco's related products; National Oilfield Volant™ (NOV) U.S. Pat. Nos. 6,443,241 and 7,096,977, and NOV's related products; Canrig™ U.S. Pat. No. 7,350,586 and Canrig's related products; Weatherford™ U.S. Pat. No. 7,191,840 and Weatherford's related products.
Basic casing operations are similar with or without the use of a top drive. Slip-type elevators are generally required to hoist more than 200 tons casing string weight. In conventional casing running operations, the traveling equipment (TD or not) only hoists the casing, with no rotational capability. Rotation for make-up is provided by a casing tong at the floor. An internally sealing packer (e.g. a Tam Packer™) may be installed on the TD quill to selectively seal inside the casing to facilitate circulation. Conventional casing running operations can only make up a casing joint; there is no capability to rotate the casing string.
Casing adaptor nubbins have been used to rotate and/or circulate casing with top drives. These are simple crossovers between the TD quill (or drillstem valve or sub) and the upper casing connection. They allow the top drive to screw into the top of the casing approximately like any drilling tubular. But it is a serious disadvantage to screw into the casing because the well owners do not want to risk any damage to the sensitive casing threads because it could compromise the integrity of the well.
The reasons well owners wish to rotate and circulate casing with the TD are known to those skilled in the art and are well covered in the CRT prior art references above, and are incorporated herein by reference.
The CRT's work reasonably well but have the following drawbacks:                a) They are expensive to purchase or to hire.        b) Although required only occasionally, they are not widely available as a service or rental.        c) They are quite complex.        d) They are separate tool to rig-up and commission.        e) They need additional load path certification & periodic re-certification requirements.        f) Heavy casing loads are transmitted through the TD's quill load path. Consequently, further drawbacks include:                    i. Strength safety factors of rotary connections are typically marginal for casing loads.            ii. Rotary connections are susceptible to cyclic fatigue effects.            iii. Drillstem valves and subs with connections matching the drill pipe typically have to be removed for the casing operation because of hoisting capacity limitations.            iv. Rotary connections cannot carry significant bending loads so they are very sensitive to misalignment during the hoisting of heavy casing loads, while typically contributing to a very stiff load path with no alignment forgiveness.                        
Top Drives may advantageously include a rotatable pipe handler section which includes: a gripper capable of clamping tubulars immediately below the TD (also called wrenches, back-up wrenches and grabbers by the various manufacturers); and, elevator links supported by structural elements capable of transmitting the elevator load directly or indirectly to the hoisting equipment (typically a traveling block).
Most top drives of which applicant is aware in the relevant class have rotatable pipe handlers for the primary purpose of actuation of the corresponding link-tilt in any plan-view orientation.
A rotatable pipe handler normally has a static or stator section anchored to the TD frame and a rotatable or rotor section containing or mounted to the elevators, elevator links and supporting structure, the link tilt actuator and the gripper. The rotatable section is typically guided on the static section by a rolling-element slewing bearing or by bushings. The rotatable pipe handlers of which applicant is aware have a capability to rotationally lock the rotatable section to the static section or the TD frame using a pipe handler lock. The pipe handler lock may include pins, tooth-engaged locks and self-locking worm gears. The locks may or may not be remotely controlled.
Many of the rotatable pipe handlers have an independently powered rotation capability, remotely controlled from the operator's station, for the pipe handler rotate function. The pipe handler rotate function typically turns the pipe handler slowly (5-10 RPM) and with very limited torque capacity (2000-3000 ft-lb max). Most of such conventional rotatable pipe handlers have a fluid rotary union (also known as rotary manifold) to transmit for example hydraulic energy (which is most common) from the static section to the rotatable section for actuation of the link tilt, gripper, etc. Elevator hoisting loads (axial) are either transmitted from the rotatable section to the static section via a thrust bearing or bushing or are transmitted from the rotatable section to the TD main shaft (quill or spindle) via a load shoulder.